1. Field of the Disclosure
The disclosure relates to a multi-antenna structure and a communication device thereof.
2. Description of Related Art
The increasing demand in signal quality, reliability and transmission speed of wireless communication signals result in multi-antenna systems being developed, for example, a pattern switchable or beam-steering antenna system or a multi-input multi-output (MIMO) antenna system. For example, the MIMO antenna technique (IEEE 802.11n) of a wireless local area network (WLAN) system band (2400-2484 MHz, 84 MHz) has been successfully applied in products such as laptops, handheld communication devices or wireless access points, and so on.
In addition to the WLAN system, a fourth generation mobile communication system (4G), for example, a long term revolution (LTE) system is also developed to be capable of achieving the MIMO multi-antenna system application. Therefore, in the future, the 4G mobile communication system can achieve greater mobile Internet capability than that of a 2G or a 3G mobile communication system. Since communication bands planned in different countries are not necessarily the same, for example, U.S.A adopts an LTE700 (704-787 MHz) band, and China and Europe respectively use an LTE2300 (2300-2400 MHz) band and an LTE2500 (2500-2690 MHz) band, and so forth. Therefore, a design challenge of the MIMO multi-antenna system is increased.
When a plurality of antennas having a same operating band are designed in a device with a limited space, if each of the antennas is required to achieve a demand of multi-band operation, problems such as multi-band decoupling may increase design complexity of the multi-antenna system.
A quarter wavelength of the 2400 MHz operating frequency of the WLAN system is about 31 mm. Therefore, the required antenna resonance size is relatively small, so that within the device, a larger space may be formed between the antennas to reduce a mutual coupling problem. However, a quarter wavelength of the 700 MHz operating frequency of the LTE700 system is about 107 mm, which is about three times greater than the quarter wavelength of the 2400 MHz operating frequency. Therefore, the antenna of the LTE700 band requires a larger resonance size for implementation, so that in the device with the limited space, a space between the antennas is shortened, which leads to increasing technical difficulty in isolation between the antennas. If an electrical connecting metal line is designed between two adjacent antennas, the isolation between the two antennas could be enhanced. However, this method is applied in single band energy decoupling rather than multi-band energy decoupling.
Another method for the single band of a shorter operating wavelength (for example, the 2400 MHz band) is designing a grounding metal structure or a slot the portions of a ground between two adjacent antennas to increase the isolation of them. However, the grounding metal structure or the slot would excite strong induced surface currents on the ground, and when the induced surface current are generated in a longer wavelength band, it may decrease the impedance matching of the two adjacent antennas.
The disclosure provides a multi-band multi-antenna system and a communication device thereof.